In some oil field service operations, such as hydraulic fracturing, cementing, acidizing and the like, high pressure fluids are pumped down the well. In some cases, the fluid pressures may be in excess of 15,000 psi. Typically, an operator brings high pressure pumping equipment to the well site and installs temporary service flowlines from the high pressure pumps to the wellhead. Because high volumes of fluid may also be needed, a number of pumping units may be connected together at one well site.
The temporary flowline components include joints or sections of steel pipe of differing lengths, various junctions, valves, swivels and the like. Generally, each well site differs, and the workers have to arrange the flowlines to extend around and past a variety of well site equipment. Many connections have to be made up, and each connection must be able to withstand the high pressure. The workers need to be able to quickly make and break out the connections to minimize the time for each job.
A hammer union is a common type of connector used for these temporary flowlines. The flowline components have ends that abut each other. A collar fits loosely on one end, the collar having internal threads for engaging threads on the end of the other flowline component. The collar has external lugs, and the workers deliver blows to the lugs to tighten the collars. While these hammer union systems work well, there are disadvantages. The larger size components can be fairly heavy, and the ends being joined have to be elevated above the ground to tighten the hammer union. A worker might sustain an injury while lifting the components and delivering blows with a hammer. In very cold climates, the hammer union could shatter or break due to the blows. Sparks can be created by delivering the blows, which could create an explosion if any combustible gas has leaked in the vicinity. The task of connecting the components with a hammer union is time consuming.
Another type of temporary oilfield service flowline uses clamps to clamp the ends of the flowlines together. The workers employ wrenches to secure four bolts that draw the clamp halves together. The clamp engages annular external flanges formed on the ends of the flowline components. A cylindrical seal recess is formed in the bore at the end of each flowline component. The cylindrical recess terminates in a shoulder that is parallel to the end face of the flowline component. A cylindrical metal carrier ring fits within but does not seal to the cylindrical seal recess. Rather a clearance exists between the recess and the carrier ring to facilitate entry of the carrier ring into the recess. Elastomeric seal rings are mounted to the carrier ring to seal against the cylindrical portions and shoulders of the recesses. This type of service flowline avoids the disadvantage of hammer union but is not in wide use.
In the clamp type of temporary flowline mentioned above, the external dimensions of the clamps are fairly large because the external flanges protrude considerably more than the outer diameter of the flowline component. Reducing the size would make setting up the flowlines more convenient because of compactness. However, the high pressure ratings mandate a certain amount of support metal and still must be maintained.
Another type of flowline connector uses clamps that secured the tubular members. In that type, the seal ring has conical surfaces that form metal-to-metal seals with conical surfaces formed in the passages of the tubular members. While able to sustain high pressures, these connectors are not normally used for oil field service work because the metal seals would not withstand daily make-up and break-out.